Automatic transmissions for motor vehicles having gearboxes comprising nested planetary gear stages are known, wherein the gearboxes' power can be transferred between one inner lying sun gear, two planetary stages and one outer lying ring gear. The planetary stages can be disposed offset to each other in the axial direction due to the tight construction space in this automatic transmission.
The document U.S. Pat. No. 5,503,605 A discloses such a planetary gearbox for an automatic transmission in which planetary gears of a first stage are engaged with an inner lying sun gear and with an inner gearing of a first ring gear. This ring gear of the first planetary gear stage has a further gearing at its outer circumference by means of which it is in effective engagement with planetary gears of a second planetary gear stage, which in turn mesh with an outer lying ring gear. The planetary gears of both planetary stages are disposed aligned behind one another in the radial direction guided by a common planet carrier, where the planetary gears of the first stage are disposed offset in the axial direction to the planetary gears of the second stage due to the prevailing conditions of the construction space. In addition, the planet carrier is composed of two individual pieces, each of which accommodate the planetary gears of a stage and are joined together in the area of the first planetary gear stage.
Furthermore, a planet carrier of a planetary gearbox can be produced by means of a primary shaping manufacturing process, as is generally known.
The two piece design of the planet carrier has the problem that the planet carrier must be joined together in an additional assembly step, which increases the expense, and reduces the load capacity of the carrier in this region. However, manufacturing such a planet carrier as one piece would make the production process much more difficult because the arrangement of the planetary gears forms an undercut. Therefore, it is necessary either to use an expensive casting procedure in which the undercut pockets of the first stage are formed using a melt-out core, or to machine cut the pockets after the casting. Both variants significantly increase the cost of production.